Security alert triggered across Punjab state after two masked men lob a grenade toward the hall belonging to the Nirankari spiritual group at a village on the outskirts of Amritsar, killing three people and wounding between 15-20 others, police say.
Three people were killed in a grenade attack on a prayer congregation in India's Punjab on Sunday which left some 20 others injured, police said.
Around 250 followers of the Nirankari spiritual group, who are considered heretics by most Sikhs, had gathered for morning prayers in Amritsar district when two men arrived and threw the explosive at them.
"Three people have died and 15-20 are injured," senior police officer Surinder Pal Singh Parmar told reporters.
The attack triggered a security alert across the state as it gears up for a major Sikh festival.
A witness said the attackers were wearing white and had covered themselves in shawls.
"Someone threw an object which flew past my neck. The explosion happened immediately," the witness told News18 network.
"Everyone started running. There was a lot of smoke."
Nirankari followers are at odds with mainstream Sikhs who dominate in Punjab.
Unlike most Sikhs, Nirankaris accept the authority of a living guru (spiritual guide).
Its members also differ from other Sikhs in their disapproval of the militant brotherhood of the Khalsa.
Punjab is gearing up for the big Guru Nanak Prakash Diwas festival on Friday.
Chief Minister Amarinder Singh condemned Sunday's attack and announced compensation of 500,000 rupees ($6,965) each to the families of the victims.
"I appeal to the people of Punjab to maintain peace in wake of Amritsar bomb blast... We will not let the forces of terror destroy our hard earned peace," he said on Twitter.
Punjab has been largely peaceful for over two decades after Indian authorities brutally suppressed a violent insurgency for an independent Sikh homeland in the 1980s and early 1990s.
The Indian military conducted a raid against Sikh separatists in the Golden Temple at Amritsar in 1984.
It was a bloody episode that angered Sikhs around the world; they accused the Indian army of desecration. The death toll in the attack remains disputed, with Indian authorities putting it in the hundreds and Sikh groups in the thousands.
Later that year, Prime Minister Indira Gandhi was assassinated by her own Sikh bodyguards, triggering a further wave of retaliation in which nearly 3,000 Sikhs were killed.